This invention relates generally to a control system for a hydraulic system having a hydraulic transformer, and more particularly, to a control system for a hydraulic system in which the hydraulic transformer has a variable pressure input.
Hydraulic transformers are useful devices in a hydraulic circuit or system. A hydraulic transformer provides pressure and flow energy transformations within the hydraulic circuit. Unlike valves, which only provide pressure reductions by throttling the flow through an orifice which incurs energy losses, the hydraulic transformer can provide an increase or decrease in pressure with corresponding increase or decrease in output flow. This is accomplished without incurring significant energy losses. Hydraulic transformers are typically used in conjunction with constant or known supply pressure as a source of power. The power source may be driven by any of a variety of prime movers such as a diesel engine, gasoline engine, piston or rotary engine, or an electric motor. The hydraulic transformers also need a hydraulic pumping device in conjunction with some type of pressure regulation system to provide the hydraulic transformers with a predetermined or constant supply pressure. This usually involves some other components such as hydraulic accumulators, pressure reducing valves, and variable displacement pumps with pressure compensation. In this manner, pump flow is adjusted to provide a constant known output pressure simultaneously with matching the output flow to the time varying demands of the hydraulic transformer connected to the hydraulic power source.
In order to provide a constant pressure to the input of the hydraulic transformer, a pumping device having some form of pressure regulation is required in combination with matching the output flow to the needs of the hydraulic system. This may require the use of pressure compensated variable displacement pumps, accumulators, pressure reducing valves or other types of pressure/flow compensation. The use of such devices are costly and create a complex system. The hydraulic system can be designed to be less complex and more economical if the supply to the hydraulic transformer can be a variable supply pressure and the flow requirements of the system are substantially matched to the flow from the hydraulic transformer. Additionally, if the speed of the machine is changed, as a result of a change in the throttle setting or as the load varies, the flow from the pump changes. By adjusting the hydraulic transformer, the flow from the transformer can be substantially matched to the flow from the pump. If the hydraulic transformer is supplied by a variable supply pressure the use of complex equipment such as hydraulic accumulators, pressure reducing valves, variable displacement pumps, and other devices necessary for maintaining a constant input pressure to the hydraulic transformer may be avoided. Simpler and lower cost power sources could then be used with a hydraulic transformer.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention, a control system for a hydraulic transformer for providing hydraulic pressure to a fluid actuator has a hydraulic system for providing a variable pressure input to the hydraulic transformer, and a controller connected to the hydraulic transformer and the hydraulic system for matching the flow demand from the hydraulic transformer to the flow produced by the hydraulic system.
In another aspect of the present invention, a control system for a hydraulic transformer providing hydraulic pressure to a fluid actuator has a fixed displacement pump for providing a variable input pressure to the hydraulic transformer, a bypass valve connected between the fixed displacement pump and the hydraulic transformer, and a controller connected to the hydraulic transformer and the bypass valve for controlling when to actuate the bypass valve to allow a portion of the fluid to be directed from the fixed displacement pump to the bypass valve.
In yet another aspect of the present invention, a control system for a pair of hydraulic transformers, a first hydraulic transformer for providing hydraulic pressure to a first fluid actuator and a second hydraulic transformer for providing hydraulic pressure to a second fluid actuator, has a hydraulic system for providing a variable pressure input to each of the hydraulic transformers, and a controller connected to the hydraulic transformers and the hydraulic system for matching the flow demand from the hydraulic transformers to the flow produced by the hydraulic system.